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Comment by _8j50 | Hacker News Reader

I thought you 0 kelvin was the lowest possible value on the kelvin scale. How come this post mention negative kelvin values? Is it not temperature?

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Interestingly, there actually is such a concept as negative temperature. It applies to systems that have a maximum allowable energy as well as a minimum one. Such systems must be isolated from the outside world, and set up carefully, but it is possible to actually get negative temperatures. https://en.wikipedia.org/wiki/Negative_temperature

I remember that from a class on lasers I took when I was an undergrad. All the physicists thought it was really cool and significant and argued about who was the first to see it coming. The engineers were totally unfazed. Whatever it takes to get the project working. And I was a would-be mathematician, so I asked whether temperature could be imaginary.

Did you get a no or something more interesting?

(I am asking for elaboration on what physicists and engineers have to say about imaginary temperatures if they didn't flatly dismiss the concept. I recognize it may read as snarky, but I really was just aiming for clever.)

No problem.

Basically the physicists thought I was winding them up and the engineers, notably including the prof, thought my priorities were all screwed up. I really did want to know the answer, but in retrospect they were both a little bit right.

If you're referring to "there will be a cosmological event horizon surrounding each observer, which will radiate Hawking radiation at a temperature of roughly 10-30 kelvin" this is a very tiny fraction: https://www.wolframalpha.com/input/?i=10%5E-30

I was referring to that, my mistake, and thank you very much!

I don't see negative Kelvin in the article. I do see Kelvins with a negative exponent, which is just a positive value that asymptotically approaches zero.

My mistake, I thought that notation implied negative numbers. Thank you.

I was saying that the temperature of the Universe in the far future will be about 0.000000000000000000000000000001 kelvin, if our current theories are correct. This is 10^(-30) kelvin.

There are no negative kelvin values in the article. 10^-30 is a positive number.

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